Higgs discovery: the beginning or the end of natural EWSB?

TL;DR

This work uses global fits to Higgs data from ATLAS, CMS and Tevatron to test the SM against a broad class of natural extensions based on composite Higgs theories. It analyzes coset-based models including SO(5)/SO(4), SO(6)/SO(5), and THDM realizations from SO(6)/SO(4)×SO(2), examining how modified Higgs couplings and additional states impact production and decay, especially h→γγ. While the SM with mh ≈ 125 GeV remains a good fit, certain composite scenarios can slightly improve the data agreement, notably via altered fermion couplings or through mixing with singlets that affect diphoton rates and potential invisible decays; yet current measurements generally prefer SM-like couplings and a minimal composite-Higgs phenomenology. The results illuminate how precision Higgs data constrain natural EWSB and help delineate which composite-Higgs constructions remain viable.

Abstract

We use global fits to analyze the most recent Higgs data from ATLAS, CMS and Tevatron and compare the Standard Model (SM) prediction with natural extensions of the SM. In particular we study wide classes of composite Higgs models based on different coset structures (leading at low energy to different Higgs sectors including extra singlets and Higgs doublets) and different coupling structures of the elementary fermions to the strong sector. We point out in what situations the composite models could improve (or worsen) the fit to the data and compare with similar trends in the MSSM.

Figures (7)

• Figure 1: In green, yellow and gray, the 68%,95%,99% C.L. contours for the parameters $a$ and $c$ with the most recent data (table \ref{['tableChannels']}). Upper plot: ATLAS with data taken at $m_h=126.5$ GeV (dashed contours correspond to data taken at $m_h=125$GeV). Lower plot:CMS with data taken at $m_h=125$GeV. A flat prior $a\in[0,3]$, $c\in[-3,3]$ is used.
• Figure 2: Global fit for the parameters $a$ and $c$, obtained combining CMS and Tevatron for $m_h=125$ GeV and ATLAS for $m_h=126.5$ (dashed circles use ATLAS at $m_h=125$ GeV); colors and priors as in fig. 1. The lines denote predictions of a generic MCHM; different curves correspond to different values of $n=0,...,5$ in Eq. (\ref{['deformation']}) ($m=0$), going downwards ($n=0,1$ correspond to the MCHM4 and MCHM5). The red part of the curves is for $0<\xi<0.25$ and the blue dashed for $0.25<\xi<1$.
• Figure 3: Tee best global fit as a function of $\alpha$ (the mixing between $h$ and the singlet $\eta$) and the ratio of the widths $\Gamma_{\eta\gamma \gamma}/ \Gamma_{h\gamma \gamma}$; here $\xi=0.25$ and $m_h=125$ GeV are fixed and a flat prior in $\alpha\in[-\pi/2,\pi/2]$ and $\Gamma_{\eta\gamma\gamma}/\Gamma_{h\gamma\gamma}\in[0,10]$ is used. Colors as in fig. 1.
• Figure 4: The $\chi^2$ for invisible branching ratio $BR_{inv}\equiv\Gamma_h^{inv}/\Gamma_h^{SM}$ for different values of $\xi=0, 0.1, 0.25, 0.5$ (solid, dashed, dotted, dot-dashed). The left plot is for $m_h=125$ GeV, the right one uses the CMS data at $m_h=125$ GeV and the ATLAS data at $m_h=126.5$ GeV. Dots correspond to the best fit points.
• Figure 5: Preferred regions in the plane $(a,c_b)$ using only the exclusive channels with associated production (CMS and Tevatron) and VBF cuts (CMS). Colors as in fig. 1. A flat prior is assumed for $a\in[0,3]$ and $c_b\in[0,3]$ (this choice for the upper limit in $c_b$ leads to the most conservative conclusions).